Method and system for enforcing access to a computing resource using a licensing attribute certificate

ABSTRACT

A licensing attribute certificate enables a trusted computing base to enforce access to a computing resource by a computer application. The licensing attribute certificate can contain enforcement data which limits the use of the computing resource. The licensing attribute certificate can also contain information allowing for the tracking of licensing data about the use of the computing resource. The use of a licensing attribute certificate to enforce access to a computing resource can allow products to be fielded which have their capability limited to a specific subset of functions. The enforcement data, the licensing data, and the data limiting the application to a specific subset of functions are cryptographically bound to the computing resource using a licensing attribute certificate according to the invention. Prior to allowing access to the computing resource by the computer application, a trusted computing base strongly authenticates that usage via the licensing attribute certificate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the authorized use ofcomputing resources by computer applications. More particularly, thepresent invention relates to use of a licensing attribute certificate(LAC) to provide cryptographic binding between a computing resource andattributes related to a computer application, and to provide strongauthentication by a trusted computing base controlling the computingresource.

2. Background Information

In a typical untrusted computer environment, a computer application canuse available computing resources with little or no authorization oraccountability. Examples of such computing resources include a modem ornetwork interface. Another example of such computing resources includesa cryptographic token, which provides cryptographic resources to thecomputer application.

FIG. 1 a depicts a typical computer system 100 made up of several“layers” 101, with two layers 130 and 132 consisting of a number ofdifferent modules 102, 103, 104, and 105. Each layer represents acollection of one or more modules at a particular abstraction level in ahierarchy of software code development. Each module represents acollection of computer instructions which perform a particular operationon the data which the module receives, producing some data output fromthe module. At the top layer 130, module 102 can represent a computerapplication running on a computer of a user 115. Via a user interface inthis example, module 102 receives input 110 from user 115. The input 110could, for example, represent ordering and payment information in anelectronic commerce transaction.

Similarly, module 103 receives data item 112, data item 114, and dataitem 116 as inputs. The module 103 processes the data items 112, 114,and 116, and produces data outputs 118 and 120. These outputs 118 and120, in turn, become inputs for computing resource A 106. Computingresource A 106 then processes its data inputs 118, 120, 122, and 124 toproduce resource output 126, which is returned to module 102.

In the example system shown in FIG. 1 a, layer 130 might be written in awell known high-level language, such as C or C++. Layer 132 can compriselibraries of lower-level functions, that would be usable by otherapplications in addition to module 102. These libraries could also bewritten in a high-level language.

In general, layer 134 represents any atomic computing resources thatprocess data. Layer 134 can be cryptographic computing resources, suchas those found on a cryptographic token. Layer 134 can also be computingresources that send signals to hardware devices, such as a display orsome other peripheral device. Layer 134 can also be computing resourcesthat transform data received from user 115.

A cryptographic token provides the ability to perform cryptographicoperations on data. Some examples of cryptographic operations includesymmetric encryption (secret key) operations, asymmetric encryption(public key) operations, key exchange operations, hash operations,digital signature operations, and key wrapping operations.

FIG. 1 b depicts an example of a system 150 of functional layers thatcontain computing resources specifically designed for providingcryptographic processing. This system, which does not contain theinvention, can be contrasted with the system shown in FIG. 4, which doescontain the invention. In the example shown in FIG. 1 b, user 152interacts with a user interface in the computer application 171 ofapplication layer 160. In this example, computer application 171represents the highest level of abstraction; that is, an interface withuser 152. As a result of input 170 from user 152, computer application171 generates inputs 172 and 174 for a mid-level application programmerinterface (API) layer 162. In this example, the mid-level API layer 162comprises two different mid-level libraries, cryptographic API library A173 and cryptographic API library B 175. These API libraries 173 and 175communicate with a low-level API library 177 in low-level API layer 164via inputs 176 and 178. Finally, the low-level API library 177communicates with the cryptographic resources via inputs 180 and 182 tosoftware drivers comprising hardware token code stack 179 or softwaretoken code stack 181 in driver software level 166. Hardware token codestack 179 interfaces with hardware cryptographic token reader 183.Hardware cryptographic token reader 183 sends data over data path 184 tohardware cryptographic token 187 in order for the data to becryptographically processed therein. The hardware cryptographic token187 contains trusted computing base (TCB) 191 which is used to providecomputing resources to computer application 171 in the form ofcryptographic operations from cryptographic computing resource A 193.Another example of a TCB which can be used to provide cryptographicoperations from cryptographic computing resource B 197 to computerapplication 171 in system 150 is TCB 195 made accessible via softwaretoken 189. Software token 189, consisting, for example, of a floppydisk, is accessed via software token code stack 181 and token reader185, and contains the necessary information to allow computerapplication 171 to access the cryptographic operations made availablevia low-level API library 177.

Early cryptographic systems used a secret key approach to secure data.In these systems, each user had the same cryptographic key which wasused for both encryption and decryption of the data. As a result, thekey needed to be kept secret or else the system could be compromised(thus the name secret key cryptography). In contrast, relatively recentadvances in cryptography have led to cryptographic systems which use amathematically related pair of keys. In these systems, one key is keptprivate by the user, while the other is made public (thus the namepublic key cryptography). These key pairs allow for algorithms thatprovide confidentiality (via encryption); and authentication, integrity,and nonrepudiation (via digital signatures).

The deployment of public key cryptography, especially in a public keyinfrastructure (PKI), relies heavily on public key certificates. Apublic key certificate (or just “certificate”) contains the public keyof a user, along with information that allows a relying party toevaluate whether or not to trust a user's digital signature producedusing the private key corresponding to that public key. In particular,the certificate contains the digital signature of a CertificationAuthority (CA). In general, the CA is a secure, standards-based, andtrusted entity that provides certificate, token, user registration, anddirectory management services. In particular, the CA issues certificatesto subscribers. A CA's signature on a certificate indicates that the CAhas verified the identity of the user whose certificate it has signed,and the CA's signature also binds the identity of the user to the publickey appearing in the certificate.

The X.509 standard of the International Telecommunication Union (dated6/97) defines an “attribute certificate” as a “set of attributes of auser together with some other information, rendered unforgeable by thedigital signature created using the private key of the certificationauthority which issued it.” Thus, an attribute certificate containsinformation to supplement the identity information in a public keycertificate.

In addition, the X.509 standard defines “strong authentication” as“[a]uthentication by means of cryptographically derived credentials”.The X.509 standard discusses the property of some public keycryptosystems (PKCSs) in which the enciphering and deciphering steps canbe reversed, and goes on to state that this property “allows a piece ofinformation which could only have been originated by X, to be readableby any user (who has possession of [the public key of X]). This can,therefore, be used in the certifying of the source of information, andis the basis for digital signatures. Only PKCS which have this(permutability) property are suitable for use in this authenticationframework.” In other words, strong authentication can only be achievedwith a PKCS in which the public key reverses the transformationaccomplished using the private key, and vice versa.

The Trusted Computer System Evaluation Criteria from the United StatesDepartment of Defense (DOD) defines a TCB as “the totality of protectionmechanisms within a computer system . . . the combination of which isresponsible for enforcing a security policy. It creates a basicprotection environment and provides additional user services requiredfor a trusted computer system.” An appropriately designed cryptographictoken can, for example, contain a TCB. Appropriate design might includefeatures such as a tamper proof case, nonmodifiable firmware, andzeroization of sensitive data upon intrusion detection. A secureoperating system is another example of a TCB.

In the past, systems have been suggested which provide access controlover various distributed computer resources. For example, in U.S. Pat.No. 5,339,403 issued to Parker, a system is described which requires auser to present a privilege attribute certificate to a computerapplication in order to access that application. However, the systemaccording to Parker assigns the privilege attribute certificate to theuser, only providing access control over the user to some subset oftarget computer applications. The system according to Parker does notprovide strong authentication as the means for allowing access from acomputer application to a computing resource. Furthermore, the systemaccording to Parker utilizes a very complex shared secret (i.e. secretkey) approach. The Parker approach relies upon encryption of theprivilege attribute certificate using the shared secret key. A secretkey system contains inherent key management problems and key compromiseproblems. In particular, a purely secret key system has no recoverymechanism following a compromise. The only way to recover (i.e. the onlyway to again provide security after compromise of a secret key) is via aphysical redistribution of secret key material.

In addition, prior systems have been developed which provide accesscontrol over portable data storage media in a manner which allowstracking the usage of certain data. For example, commonly owned U.S.Pat. No. 5,457,746 issued to Dolphin on Oct. 10, 1995, describes asystem which allows a publisher to define and enforce attributes relatedto encrypted files stored on external media. The attributes in thissystem could relate to such things as usage of particular data,time-related usage of a resource, or number of log-ons.

For many reasons, it is desirable to control the use of computingresources by a computer application through the use of strongauthentication. For example, certain computing resources available oncryptographic tokens, if accessible by the computer application, wouldrender the token unable to be exported from certain countries (such asthe United States) unless restricted to use by approved computerapplications. If those cryptographic operations could be successfullylimited to use by approved computer applications using strongauthentication, the cryptographic token could then be exported.

Similarly, it may be desirable to limit the accessibility tocryptographic operations contained in a cryptographic token forlicensing reasons, which would require a metering of those operations.For example, a provider of cryptographic products might desire to limitaccess to operations on a cryptographic token to those entities who haveproperly licensed those operations from the provider. Alternatively, itmay be desirable for developers of software products to controlaccessibility to their products using strong authentication techniquesprovided by the use of an LAC, in conjunction with separate computingresources.

SUMMARY OF THE INVENTION

According to the invention, a licensing attribute certificate (LAC)enables strong authentication techniques to be utilized for enforcingaccess to computing resources, via the use of standards-based public keytechniques. Enforcing can include, for example, controlling access tocomputing resources, metering usage of computing resources, selectivelyenabling certain functions available from computer resources, or anycombination of these and other functions. The LAC can containinformation allowing for the tracking of licensing data about the use ofcomputing resources. Those computing resources can be contained within atrusted computing base (TCB). The TCB can be in any of a number offorms, including contained within a cryptographic token or a secureoperating system. The LAC can further contain information which limitsthe use of the available computing resources. This would allow productsto be fielded, such as cryptographic tokens which contain cryptographiccomputing resources, which have their capability limited to a specificsubset of functions. The use of a LAC in accordance with the inventioncan provide a cryptographically strong way of limiting access by acomputer application to a specific subset of functions.

In one embodiment of the invention, a computer application developerreceives a LAC from a vendor of a computing resource. A vendor caninclude any person or entity which provides computing resources. Thedeveloper embeds the LAC, containing a vendor's digital signature, intoa computer application. The public key corresponding to the vendor'sprivate key can be built in to the software library that provides theinterface between the computer application and the TCB. Alternatively,the public key corresponding to the private key of the vendor can bebuilt in to the TCB containing computing resources.

In yet another embodiment, separate public keys can be built in to boththe software library and the TCB. When the computer application attemptsto use a computing resource within the TCB, the library seeks to verifya first digital signature of the vendor and the TCB seeks to verify asecond digital signature of the vendor. In addition to checking thatboth of the digital signatures are valid, checks could be made on theenforcement data within the licensing attribute certificate to determinewhether access to the computing resources within the TCB can take place.

This invention provides a method for enforcing access by a computerapplication to a computing resource controlled by a trusted computingbase, using standards-based public key techniques. The invention usesstrong authentication to enforce that access control. The invention thusovercomes the complexities in the data exchanges involved in prior artsystems. The invention also provides strong authentication in the use ofa computing resource by a computer application, and eliminates thesecurity risks particularly associated with systems which implementsecret key approaches. The invention also provides a method for trackingusage of a computing resource using a LAC. Furthermore, the inventionprovides a method for allowing computer application developers tocontrol access to their products via use of a LAC. In addition, theinvention provides a method for restricting the usage of a computingresource to authorized functions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a and FIG. 1 b depict the arrangement of software modules inlayers, including software layers that contain particular elements forproviding cryptographic processing.

FIG. 2 depicts a basic architectural diagram showing a licensingattribute certificate that has been installed in equipment belonging toa user.

FIG. 3 a, FIG. 3 b, and FIG. 3 c depict a method, according to theinvention, of using a licensing attribute certificate tocryptographically bind information about a computer application andcomputing resources contained within a trusted computing base.

FIG. 4 depicts an example, according to the invention, of thecryptographic binding between a computer application and a trustedcomputing base which provides cryptographic resources.

FIG. 5 depicts the contents of one embodiment of a LAC.

FIG. 6 depicts a process, according to the invention, of producing thetoken related information in the licensing attribute certificate.

FIG. 7 depicts a process, according to the invention, of producing thelibrary related information in the licensing attribute certificate.

FIG. 8 depicts a library enforcement process, according to theinvention.

FIG. 9 depicts a token enforcement process, according to the invention.

FIG. 10 depicts an example, according to the invention, of a tokenenforcement process which checks a counter to determine whether or not acertification authority can issue a certificate.

FIG. 11 a and FIG. 11 b depict two models of licensing attributecertificate implementation, according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, a method and system forcryptographically binding a computing resource and a licensing attributecertificate (LAC) allows only authorized usage of the computingresource. The computing resource can, in one embodiment, be locatedwithin a trusted computing base (TCB). In another embodiment, thecomputing resource can be located outside of the TCB. In either case,the operations available from a computing resource cannot be accessedwithout a cryptographic verification by the TCB of the computerapplication's use of that computing resource. In a further particularembodiment, a LAC is used to provide strong authentication of acomputing resource by a cryptographic token via a digital signature.

FIG. 2 depicts a basic system involving a LAC, according to theinvention. User equipment 205 contains TCB 208, computer application210, and LAC 220. User equipment 205 can include any type ofcomputational device. Some examples include a personal computer, apersonal digital assistant, or a machine with embedded computingcapability. In general, user equipment represents any equipment used bya person or other entity (such as a corporation) that contains at leastone computer application and at least one computing resource.

LAC 220 in FIG. 2 contains attribute information about computingresource 226, in the form of enforcement data 222. Enforcement data 222facilitates enforcement of the use of the computing resource and cancontain, for example, information about how and when the computingresource can be used. Enforcement data 222 can further containinformation about what operations available from the computing resourcecan be used. LAC 220 also includes digital signature 224 computed usinga private key.

TCB 208 in FIG. 2 contains computing resource 226, to which TCB 208controls access, as represented by the switch in data path 230. TCB 208also contains a public key 212, corresponding to the private key thatwas used to compute digital signature 224. Prior to computer application210 gaining access to computing resource 226, TCB 208 must authenticateLAC 220 using public key 212. If the authentication of LAC 220 succeeds,TCB 208 will permit computer application 210 to access computingresource 226 along data path 230.

FIG. 3 a depicts a method according to the present invention as appliedto enforcement of authorized usage (e.g. licensing) of computingresources. Other applications of the invention can include, for example,exportability compliance or allowing selective usage of a computingresource.

In FIG. 3 a, vendor 301 of a computing resource 360 (shown in FIG. 3 c)first produces enforcement data 312 that can, for example, correspond toparticular rights afforded to a specific computer application developer303 (shown in FIG. 3 b). For example, the vendor of a computing resourcemight wish to limit the access to that computing resource to only acertain application. Alternatively, the vendor of the computing resourcemight wish to grant access to a subset of all of the functionalityavailable from the computing resource. For example, where the computingresource is a hardware cryptographic token, the vendor might wish toonly allow digital signature operations to be executed and wouldtherefore need to disallow encryption operations.

In FIG. 3 a, vendor 301 uses its private key 310 to compute digitalsignature 316 on enforcement data 312 using sign process 314. Signprocess 314 (as well as other sign processes discussed herein) can beimplemented using any of the well understood techniques for computing adigital signature. For example, the Digital Signature Algorithm, asspecified in Federal Information Processing Standard Publication (FIPSPUB) 186 could be used to calculate digital signature 316.Alternatively, the RSA algorithm could be used.

Digital signature 316, corresponding to the particular computingresource 360, is combined with enforcement data 312 to form LAC 318.Vendor 301 then transmits LAC 318 to computer application developer 303.The transmission of LAC 318 to computer application developer 303 canoccur using any methods and apparatus, including both networked andnon-networked approaches. The LAC could be sent via a network, such as,for example, a Local Area Network (LAN), a Wide Area Network (WAN), orvia the Internet. Transmission methods can include such things as, forexample, electronic mail from the vendor to the computer applicationdeveloper. Alternatively, the LAC can be posted on a bulletin boardsystem (BBS), or can be stored in a directory of a computer system bythe vendor and retrieved by the application developer using any type ofretrieval technique, such as, for example, Telnet.

In FIG. 3 b, computer application developer 303 generates computerapplication source code 330, which is combined with LAC 318. Computerapplication source code 330 and LAC 318 can be combined by using compileprocess 332, which creates an association between the computerapplication source code 330 and LAC 318. In another embodiment, acomputer application and a LAC can be combined by providing an entry ina system registry of a computer operating system.

In FIG. 3 b, the compilation of computer application source code 330 andLAC 318 generates an executable application 334 which can containcomputer application 333 with LAC 318 embedded within it. Once compiled,the executable application 334 can be made available for distribution tousers.

In FIG. 3 c, user 305 can acquire the executable application 334 (which,in this example, contains the version of computer application 333 thatcan be executed on a computer) through any of several means including,for example, retail store purchase, electronic purchase (e.g., via theInternet), or any other software distribution mechanism. User 305 canmake a purchase of, for example, a CD-ROM containing executableapplication 334, or can purchase and then download executableapplication 334 electronically. User 305 loads executable application334 onto the user's computer 340 and runs executable application 334. Inthis example, executable application 334 needs to utilize computingresource 360 contained within TCB 345 (which can be contained withincomputer 340).

However, in order to gain access to computing resource 360, digitalsignature 316 contained within LAC 318 must be verified by TCB 345. TCB345 performs verify process 370 using public key 354 in combination withenforcement data 312 to verify digital signature 316. The success ofverify process 370 means that digital signature 316 in LAC 318 is valid.In addition, supplemental enforcement data 356, which may be containedin a database within computer 340 (i.e. external from the LAC), could beutilized to provide further control over accessibility to computingresource 360 as further described with reference to FIG. 10. Once LAC318 is validated, executable application 334 being used by user 305 willthen have access to computing resource 360.

In order to verify digital signature 316, TCB 345 must have public key354. In one embodiment, depicted in FIG. 3 c, vendor 301 can embedpublic key 354 in TCB 345. In an alternative embodiment, TCB 345 canreceive public key 354 via a separate X.509 identity certificate pathwhich is transmitted along with LAC 318.

FIG. 4 depicts a system 400 according to one embodiment of the inventionwhich includes computing resources specifically designed for providingcryptographic processing. This embodiment represents one aspect of theSPYRUS S2CA, made and sold by SPYRUS, Inc. of Santa Clara, Calif., whichis a secure, standards-based, and trusted certification authority (CA)that provides certificate, token, user registration, and directorymanagement services.

In system 400 in FIG. 4, user 480 installs and runs executableapplication 411 on the user's computer. Executable application 411 cancontain a number of different types of computer functionality, includingsuch things as user interfaces, software libraries, and device drivers.In this example, the executable application 411 can contain LAC 403which can be embedded in computer application 402. Also included inexecutable application 411 can be executable libraries, including PKCS#11 application programmer interface (API) 404 and Microsoft CryptoAPI(CAPI) 406. PKCS #11 is a nonproprietary, technology-neutral programminginterface for cryptographic tokens such as smart cards and PCMCIA cards.CAPI is an interface that allows developers to build applications thatuse system-level certificate management and cryptography.

Computer application 402 communicates with PKCS #11 API 404 via datapath 412 and with CAPI 406 via data path 414. Upon execution ofparticular instructions in either PKCS #11 API 404 or CAPI 406 whichrequire functionality contained within cryptographic computing resource484, LAC 403 can be passed via either data path 416 or data path 418 tothe vendor specific library, such as the SPYRUS Extensions (SPEX)library 408.

In FIG. 4, SPEX library 408 performs library authorization 800 which caninclude using library public key 410, library supplemental enforcementdata 417, and LAC 403 in verify and validate process 415. Further detailon library authorization 800 can be found in FIG. 8. The libraryauthorization step provides an interim level of enforcement that doesnot involve a cryptographic token at all. This can be useful, forexample, for minimizing the number of operations to be performed by thecomputing resources. As long as verify and validate process 415succeeds, SPEX library 408 will be permitted to communicate withhardware token code stack 430, in attempting to make use ofcryptographic computing resource 484. In this example, cryptographictoken 470 contains cryptographic computing resource 484 which SPEXlibrary 408 accesses via hardware token code stack 430 and smart cardreader 460.

In this embodiment, control of the use of the cryptographic operationswithin the cryptographic computing resource 484 occurs within theboundaries of TCB 474 which is contained within cryptographic token 470.These cryptographic operations can be carried out on a cryptographictoken. For example, a LYNKS PCMCIA card or a Rosetta smart card, bothmade and sold by SPYRUS, Inc. of Santa Clara, Calif., provides all ofthe above mentioned cryptographic operations to a computer application.Other examples of a hardware cryptographic token include a separatehardware board inside of a computer or an external hardware peripheraldevice. Alternatively, these cryptographic operations can be carried outvia the use of a software cryptographic token, which can comprise acomputer processor executing instructions and accessing data stored on adata storage device such as a floppy disk. For example, the softwareversion of the Fortezza™ cryptographic token, also made and sold bySPYRUS, Inc. of Santa Clara, Calif., provides all of the above mentionedcryptographic operations to a computer application.

Prior to allowing any use of the cryptographic operations available inthe cryptographic computing resource, TCB 474 performs tokenauthorization 900 (described further below with respect to FIG. 9) whichincludes using token public key 490, token supplemental enforcement data477, and LAC 403 in verify and validate process 482. The success ofverify and validate process 482 confirms the cryptographic bindingbetween cryptographic computing resource 484 and LAC 403. This allowsTCB 474 to enforce the proper use of the cryptographic operationscontained in cryptographic computing resource 484 by computerapplication 402.

The enforcement of the proper use of the cryptographic operationscontained in cryptographic computing resource 484 can occur via theenforcement data contained in LAC 403. Enforcement data permitsenforcement of various conditions represented by the data. Enforcementdata can, for example, be defined such that computing resources are onlyavailable for a specified number of uses, or such that only certainfunctions within the computing resources are available. The bit patternin the LAC in FIG. 5 represents one embodiment of the data used toprovide enforcement. In another embodiment, a LAC can be implementedusing the X.509 attribute certificate format.

LAC 403 in FIG. 5 contains enforcement data 520 which can includeattribute data associated with both cryptographic token 470 and SPEXlibrary 408. Token attribute data 502 can, for example, identify thecryptographic operations on token 470 which are available to computerapplication 402 via SPEX library 408. Token digital signature 504 can beused by token 470 to validate token attribute data 502 and to enforcethe proper use of the cryptographic operations by computer application402. Library attribute data 506 can represent the functionalityavailable to computer application 402 via SPEX library 408. Libraryattribute data 506 can be further logically divided into accessibletokens data 508 and sub-functionality data 510. These can allow evenfiner granularity to be defined for the subset of functions identifiedby library attribute data 506. For example, sub-functionality data 510can be used in enforcing the available SPEX library functions such as,for example, limiting the functions available to computer application402 to only encryption and decryption, but not authentication.

In addition to the attribute data, LAC 403 in FIG. 5 contains librarydigital signature 514. Library digital signature 514 can allow the SPEXlibrary 408 to validate the LAC, and thereby control the availability ofthe library's functions.

FIG. 6 depicts a first step in the assembly of LAC 403 according to anembodiment of the invention. First, the computing resource vendorgenerates token attribute data 502 associated with the particularcomputer application for which the LAC is being created. Once tokenattribute data 502 has been determined, the vendor uses token privatekey 602 to digitally sign token attribute data 502 using sign process604 which produces token digital signature 504.

Next, the vendor specifies information that determines the accessibilityto the functions on the token. In the LAC 403, accessible tokens data508 represents this information. The vendor of cryptographic tokens candefine, for example, accessible tokens data 508 such that access to thecomputing resources would be limited to only those resources on thatvendor's cryptographic tokens. After accessible tokens data 508 has beengenerated, the vendor then sets sub-functionality data 510 which canallow even finer granularity enforcement of the available resources.Once assembled, token attribute data 502, token digital signature 504,accessible tokens data 508, and sub-functionality data 510 compriseenforcement data 520.

FIG. 7 depicts a subsequent step in the assembly of LAC 403 in thepresent embodiment. Once all of the enforcement data 520 associated withthe token and the library has been generated for LAC 403, the vendoruses a library private key 702 to digitally sign enforcement data 520using sign process 704. The result is library digital signature 514,which is then appended to enforcement data 520. The overall dataassembly, consisting of token attribute data 502, token digitalsignature 504, accessible tokens data 508, sub-functionality data 510,and library digital signature 514 comprise LAC 403.

It may be desirable to use two different key pairs (each consisting of apublic and a private key) for the two signing processes 604 and 704 inFIG. 6 and FIG. 7, respectively. This means that token private key 602in FIG. 6 and library private key 702 in FIG. 7 are different. This maybe the case, for example, if the vendor of the token differs from thevendor of the library. Alternatively, the two key pairs (and thus thetwo private keys 602 and 702) can be the same. This may be the case, forexample, if one vendor distributes both the token and the library.

FIG. 8 illustrates library authorization process 800 performed by SPEXlibrary 408, as discussed generally in regards to verify and validateprocess 415 shown in FIG. 4. Upon receiving LAC 403, SPEX library 408separates library digital signature 514 from the remainder of LAC 403.The enforcement data 520 is input to verify process 840, along withlibrary digital signature 514 and library public key 410. If the librarydigital signature 514 is properly verified, the library 408 permitsprocessing to continue. If the library digital signature 514 is notproperly verified, SPEX library 408 notifies computer application 402that an error has occurred. If an error does occur, the library can takea variety of courses of action such as using an alternate resource.

Once library digital signature 514 has been verified, the library 408checks library attribute data 506 against library supplementalenforcement data 417. This can, for example, determine whether thelibrary 408 is permitted to access the token or tokens designated in theaccessible tokens data 508 and determine whether library 408 can performthe particular operations designated in sub-functionality data 510. Ifthe validation of either accessible tokens data 508 or sub-functionalitydata 510 fails, data path 860 will not be enabled, which will prohibitthe library 408 from further communications with the cryptographic token470.

FIG. 9 illustrates token authorization 900 performed by token 410, asdiscussed generally in regards to verify and validate process 482 inFIG. 4. The token 470 separates the token digital signature 504 from LAC403. Token attribute data 502 is input to verify process 940, along withtoken digital signature 504 and token public key 480. If the tokendigital signature 504 is properly verified, the token 470 permitsprocessing to continue. If the token digital signature 504 is notproperly verified, the token 470 notifies library 408 that an error hasoccurred. Library 408 then notifies computer application 402 of theerror, and computer application 402 will handle the error. Computerapplication can notify user 480 of the error, or can attempt to processthe error without notifying user 480.

Once token digital signature 504 has been verified, token 470 checkstoken attribute data 502 against token supplemental enforcement data 477in validate process 950. This determines whether token 470 is permittedto perform the particular operations designated in token attribute data502. If the validation fails, data path 960 is not enabled, which willprohibit the use of token 470 by computer application 402.

FIG. 10 depicts LAC 1000, according to an embodiment of the invention,which can be used for tracking usage of a particular computing resource.In this embodiment, the LAC 1000 exists in a system at a certificationauthority (CA) which issues certificates. In FIG. 10, token attributedata 1070 contained in the LAC can contain usage data for a computingresource. This usage data allows the usage of the computing resource tobe metered. For example, token attribute data 1070 in FIG. 10 contains amaximum certificates to issue field 1072. Token supplemental enforcementdata 1074, which resides in a database that can be maintained outside ofa TCB, contains certificates issued counter 1076. Certificates issuedcounter 1076 reflects the number of certificates that have been issuedby the CA. During validate process 1050, maximum certificates to issuefield 1072 is compared against certificates issued counter 1076. Ifcertificates issued counter 1076 has exceeded the value in maximumcertificates to issue field 1072, further usage of the computingresource will be disallowed.

The check of certificates issued counter 1076 against maximumcertificates to issue field 1072 can occur inside of the TCB. Oncechecked, the TCB would then update certificates issued counter 1076,store the updated value within the TCB, and send the updatedcertificates issued counter 1076 back to the database. In an alternativeembodiment, the updating of the certificates issued counter 1076 canoccur external from the TCB.

In another embodiment, the usage data can, for example, correspond to amaximum number of accesses by a computer application to a computingresource. In yet another embodiment, the usage data can, for example,correspond to a maximum number of cryptographic operations that can beperformed by computing resource which provide cryptographicfunctionality.

The embodiments of the LAC described so far represent only a few of manypossible models of LAC usage. As the model in FIG. 11 a shows, vendor1101 can distribute LAC 1102 (comprising enforcement data 1104 anddigital signature 1106) to application developer 1108. Applicationdeveloper 1108 creates computer application 1112 into which LAC 1102 isembedded, as previously described. Vendor 1101 also distributescomputing resource 1115 and vendor public key 1119 (both containedwithin TCB 1110) to the user, who installs the TCB 1110 in userequipment 1114. The user also installs computer application 1112,containing LAC 1102, in user equipment 1114. Prior to being able to usecomputing resource 1115, however, TCB 1110 would need to properlyvalidate LAC 1102 using vendor public key 1119 contained in TCB 1110.

FIG. 11 b shows a model which differs somewhat from that shown in FIG.11 a. In FIG. 11 b, application developer 1120 creates computerapplication 1122 and has no interaction at all with vendor 1101. Incontrast to the model in FIG. 11 a, the user sends request 1124 fromuser equipment 1114 to vendor 1101. In response, vendor 1101 preparesLAC 1103 and transmits this directly to the user. The user installs bothLAC 1103 and TCB 1110 on user equipment 1114, in addition to computerapplication 1122. In this model, similar to the model shown in FIG. 11a, prior to being able to use computing resource 1123, TCB 1110 mustproperly validate LAC 1103 using vendor public key 1121.

Although the invention has been described for a licensing attributecertificate used by a CA, it applies to a wide range of computingapplications where enforcing authorized usage of resources is desired.For example, usage of computer aided drawing (CAD) software could beenforced with a LAC. In addition, access to a CD-ROM containing datacould be enforced with a LAC. Thus, the present invention is not limitedto the precise embodiments described above. For example, while a LACcould be compiled with a computer application as described above, asystem and method according to the invention could just as easily beimplemented in which a LAC exists in a separate file from an executableapplication. Similarly, other authentication means besides digitalsignatures could be used. Additionally, the counter discussed in themethod for using a LAC to track usage of a resource might be containedwithin the cryptographic token itself.

It is clear that various changes and modifications may be made to theembodiments which have been described, more specifically by substitutingequivalent technical means, without departing from the spirit and scopeof the invention. The embodiments presented are illustrative. They arenot intended to limit the invention to the specific embodimentsdescribed and shown in the attached figures. Instead, the invention isdefined by the following claims.

1. A method for enforcing access by a computer application to acomputing resource controlled by a trusted computing base, comprisingthe steps of: generating enforcement data identifying usage of saidcomputing resource; embedding said enforcement data in a licensingattribute certificate; cryptographically binding said licensingattribute certificate to said computing resource using a private key;associating said licensing attribute certificate with said computerapplication; and authenticating in said trusted computing base the useof said computing resource by said computer application using a publickey corresponding to said private key. 2-47. (canceled)